High-temperature cobalt alloy



Patented July 18, 1950 HIGH TEMPERATURE COBALT. ALLOY Edward Epremianpschenectady 36.; assignorr; to? Genera-[:Electricicompany ra ecorporation of; r

New :Yorle Nd'nl'awinga Application-Jul 15; I

Serial'No. 761,161'

' 2"Gla/ims. 1' (Cl. 75-171) The present invention? relates to; a shigh -temeu perature; high-strength cobalt; alloy: Itais :par-c ticularly concerned with a heat and corrosion-1 resistantalloy. particularly adapted: for::fabrication. of the buckets'iand other working parts 1 of gas turbines and the like.

:my; pri or application Serial "No 592 ,08 9;:fi1ieeh May 5; 1945, now abandoned,.andEassigned: 1301121131 same: assignee as the present invention; thereqisi disclosed and claimed: a" cobalt alloy. containing: substantial quantitiesof: chromiummandl nickel? and "a 'lowcarbon content; the inicirelwcontentcof the alloy preferably ranging from 9-11;%' ;1 in, order toobtainiauproduct which has desirable high-temperature characteristics and which can also be welded.

The-present inventionrelates tor-an alloy of the type disclosed in my prior z-appl-ication; and" is based on the discovery. that bydecreasing the preferred nicked content to 4-6%, decreasing the chromium content to 19-21%; holding the carbon content-within the -range 0.254137%, and" adding; titanium and-"boronamounts 'ranging from 0.254% -titanium--- and 0.02-0.1-boron, there A can be obtained analloy possessing 'exceptional strength andductility at elevated temperatures? The-alloy displays-"these excellent properties "in the as cast-conditionand does :not require heat treatment;-

In carrying out the present, invention, I,employ a cobalt base alloycontainingabout19-21% chromium, 443% nickel, 3."5=4:5% tungsten, 35-45% molybdenum, 0.'25+0;-7%i;': preferably 0.250.4% carbon,- 0.2=1% titanium, and,.0.02-0.1,% boron, balance substantially. cobaltf except" for, up to 4% iron added with the titanium and boron and deoxidizing quantities of manganese and silicon, these latter elements being present in amounts not exceeding 1% of each.

The titanium and boron can be added to a melt of the principal ingredients in the form of ferrotitanium and ferroboron. However, due to the fact that the titanium in the form of ferrotitanium is somewhat troublesome in melting, both the titanium and boron are preferably added in the form of a commercially available alloy known as Carbortam, an alloy of about 18.8% titanium, 2.87% silicon, 5.4% carbon, 1.2% boron, balance iron. This alloy dissolves with relative ease in a melt of the remaining ingredients and serves as a means for introducing titanium and boron in substantially the desired proportions.

The addition of titanium and boron is known to have a profound eifect upon the high-temperature strength of various alloys particularly with regards to the rupture and creep properties. While a number of interesting alloys containing titanium and boron have been produced; none of them have proved to be of particular practical value due to the fact that they exhibited both a present invention containing both of: theses ele;-

ments :isnexceedingly ductile c: and-x, exhibits Q1101 tendency to; become; brittle-whensubjected. to; elevated: temperatures -forrlong periods of time;

The present alloy-is: easily prepared b'yz-the:

usual methods: and ofiers no; particular difiicuL,

tieslinpcastin'g For; example;, the :alloycan be: prepared by making a melt of: the cobalt,: nickel;- moyb'denum; tungsten; chromium, carbon, man-1 ganese silicon;:andjfinally adding the commercial titanium-boron-iron;alloy; the 1 latter being dropped beneath the surface of the melt so that the lumps thereof are coated with metal to prevent oxidation& of: the; titanium, during, solution of the alloy.- A preferred alloy hereafter referred to as X521] preparediin-this manner contains about,20%j chromium; 5% nickel, 4% tungsten,

4%1molybdenum, 4% iron, 0.5% manganese,.0.5% silicon, 0.401% carbon,-. 0.33% titanium, 0.06%

1" boron andbalancecobalt; This alloy has been.

found to'ha've a hour rupture strength (R. S.) of 32,500 lbs. per square inch and an elongation of 23% at a temperature of l500 F. The 1,000- hour..rup.ture. strengthmat this temperature was 26,000,.v lbs..per; square, inch and its elongation 23%... The. rupturewtest, by which the rupture strength figures...were-obtained consists of imposing a constant load on. a sample of the alloy ata constant temperature.. The variable involved,

in this test is the time required for fracture. The'data obtained fromseries; of such tests employing; difierent loadsi at the same temperature aretheni plottedin curvesxof, log stressversus log time: From these curves the strengthuof the 1 material can be reported asthe 100-houror 1,000.-

hour rupture strength, that is the stress'which will producefailure in the alloy in 100 hours or 1,000'hours atth'e particular test temperature;

The above-describedalloy X52D was also compared with a similar alloy prepared without the addition of"Carbortam-, with thefollowing re: sul-ts aha-temperature ot-150091 .for. 100 hoursz:

R". ,S.',; Percent p. s. i-., I E]...

X52D 500 23 X52D without Carbortam addition 27, 000 12 Although difficulty has previously been experienced with alloys strengthened by theaddition of titanium and boron in the loss of considerable titanium and boron upon remelting of the alloys, so that such alloys did not lend themselves to casting procedures involving the re- Chemical analysis showed that there was no change in composition except that the carbon content had increased to about 0.40% and the titanium decreased to 0.30%.

Preferably the alloy of the present invention is precision cast, for example, as turbine buckets by pouring at any temperature of from 1500- 1700 C. into molds'held at temperatures not substantially exceeding 750 C. The optimum casting conditions depend upon the specific part which is being produced. A comparison of the compositions and properties of the alloy X52D, within the scope of the present invention, with closely related alloys differing only in their nickel, molybdenum, or tungsten contents can be made from the following tables, in which Table 1 lists the compositions of the alloys and Table 2 the results of rupture tests. The carbon and titanium values given in the table are all actual determinations, while the others are nominals which were spot checked and found to be within the range of experimental error:

Table 1 OM11 SiCrNiMoWTiB Fe .5 .5 20 6 .30 .06 ha]. 4 .5 .5 20 '6 .28 .06 hill. 4 .5 .5 2O 10 4 4 .39 .06 ha]. 4 .5 .5 5 4 4 .33 .06 bal. 4 .5 .5 20 5 6---- .42 .06 bal. 4 .5 .5 20 10 6 .33 .06 bal. 4

Maximum.

Table 2 100 hours 1,000 hours B. S Per Cent R. S Per Cent p. s 1 El. p. s 1 El.

20 14 27 25,500 20 23 26,000 23 25 24,500 18 X52F 27 X52D (remelted from master heat) 34,000 20 27,000 20 Y52A X5213 15,500 27 X520 14,500 24 X521)- ,000 33 X52E, 14,500 X52F-- ,000 22 X52D (rernelted master heat) 17,000 25 From the tabulated test data it will be seen that while most of the compositions listed possess high rupture strength and excellent ductility, best results are obtained when the chromium, nickel, molybdenum and tungsten are present within the range of proportions specified hereinbefore.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A heat and corrosion-resistant alloy characterized by good rupture strength and ductility at elevated temperatures, said alloy containing 19-21% chromium, 4-6% nickel, 3.5-4.5% molybdenum, 35-45% tungsten, from 0.25 to 0.7% carbon, from 0.2 to 1% titanium, 0.02 to 0.1% boron, not over 4% iron balance cobalt except for manganese and silicon in deoxidizing quantities less than 1%.

2. A heat and corrosion-resistant, high-temperature cast alloy containing from 0.25 to 0.4% carbon, manganese and silicon in deoxidizing quantities less than 1% of each, about 20% chromium, about 5% nickel, about 4% of each of the elements tungsten and molybdenum, not over 4% iron, from 0.2 to 1% titanium and 0.02 to 0.1% boron, balance cobalt, said alloy being characterized by good rupture strength and ductility at 1500 F.

EDWARD EPREMIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Metals Handbook, 1939, page 506, pub. by Amer. Soc. for Metals, Cleveland, Ohio. 

1. A HEAT AND CORROSION-RESISTANT ALLOY CHARACTERIZED BY GOOD RUPTURE STRENGTH AND DUCTILITY AT ELEVATED TEMPERATURES, SAID ALLOY CONTAINING 19-21% CHROMIUM, 4-6% NICKEL, 3.5-4.5% MOLYBDENUM, 3.5-4.5% TUNGSTEN, FROM 0.25 TO 0.7% CARBON, FROM 0.2 TO 1% TITANIUM, 0.02 TO 0.1% BORON, NOT OVER 4% IRON BALANCE COBALT EXCEPT FOR MANGANESE AND SILICON IN DEOXIDIZING QUANTITIES LESS THAN 1%. 